It's great to see this landmark work on extinct birds is finally online. But there must be also some place for a critical review. First, i must say Rothschild has compiled a lot of species which were unknown to Rothschild's time. He wrote about species from Museum collections which have been never described before and after his work. He described so called hypothecial species which are only based on paintings or oral reports. Compared with our current knowledge several described taxa must be now regarded as invalid like Astur alphonsi (a raptor which is only known by some bones from Mauritius but is in fact from the Mauritian population of Circus mallardi). Further Rothschild named all known Moa taxa and synonyms. But thanks to paleontological work of Trevor H. Worthy we are knowing that most moas which were described as distinct species to Rothschild's time were the females of another moa species as these were about three times larger than the males. Rothschild missed several species which were even considered as almost extinct to his time (1907) like the Passenger Pigeon, the Heath Hen, or the Carolina Parakeet. There 45 beautiful color paintings and 4 b/w sketches by John Gerrard Keulemans, George Edward Lodge, Henrik Grönvold, Frederick William Frohawk, and Joseph Smit.